In: Biology
Describe the mitochondrial electron transport pathway and the synthesis of ATP by mammalian mitochondria.
Describe the urea cycle including its function, energy costs and regulation.
If palmitic acid (16:0) labeled in C-1 were metabolized under anaerobic metabolism in mammalian tissues, what carbon atom would be tagged with 14C in what compound?
Electron transport chain is the last process of cellular respiration which takes place in inner mitochondrial membrane. The ultimate goal of electron transport chain is to synthesise ATP. ATP is the energy currency of the cell which is used by the cell to perform its metabolic activities.
Electron transport chain begins with the donation of electrons by high energy electron carriers, NADH and FADH2 which are synthesized during glycolysis, pyruvate oxidation and citric acid cycle of cellular respiration. These electrons are then passed on from one electron carrier to the other.
All the electron carriers are transmembrane protein molecules except for ubiquinone and cytochrome C which are peripheral membrane proteins. All the electron carriers are arranged in increasing order of their electrode potential. As the electrode potential increases, the affinity of an electron carrier for electrons also increases.
Ultimately the electrons are accepted by oxygen which gets reduced to form water. Water is a byproduct of cellular respiration.
When electrons are transferred from one electron carrier to the other, protons are also pumped from mitochondrial matrix to intermembrane space. This leads to an increase in the concentration of protons in intermembrane space thereby increasing its acidity. This results in the formation of a differential concentration of protons on both the sides of the membrane and development of a proton gradient.
The electrochemical energy stored in proton gradient is used by ATP synthase enzyme for the phosphorylation of ADP into ATP. This occurs when protons are diffused back into the mitochondrial matrix by ATP synthase enzyme. This results in the spinning of enzyme and formation of ATP.
This is called as oxidative phosphorylation, formation of ATP in the presence of oxygen. This is also called as chemiosmosis because the energy stored in ionic gradient of protons is utilised for the formation of a molecule which is ATP in this case.
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